Sorry again, I posted an hour ago and it's disappeared... Anyway, thanks to Mick for sending me a link to the Beverley Sisters' version; now I recognise the tune. It is indeed the White Rose Of Athens, but with different lyrics, not the original translation which goes "When the white rose blooms again..." - as here: The White Rose Of Athens. It looks like Newell wrote a new, unrelated set of lyrics using the old tune to create The Water And The Wine.

Mystery solved...